The present invention relates to a shock absorber for a wheeled vehicle such as a motorcycle of automobile. A typical shock absorber to which the present invention constitutes a novel and unique improvement is disclosed in U.S. Pat. No. 4,108,287, issued Aug. 22, 1978 to Tetuo Kato, and entitled "DOUBLE-CYLINDER BUFFER".
A piston is sealingly slidable in an inner cylinder and is connected at its upper end to a frame of the vehicle through a piston rod. The lower end of the inner cylinder is closed and connected to an axle of the vehicle. The piston is provided with valves to allow restricted fluid flow therethrough for damping relative movement between the frame and axle. An outer cylinder is coaxially disposed around the inner cylinder and communicates at its lower end with the inner cylinder. The inner cylinder is filled with liquid such as hydraulic fluid. The lower portion of the outer cylinder is filled with the liquid. The space in the outer cylinder above the liquid is filled with a gas such compressed air.
The outer cylinder acts as an overflow reservoir for the inner cylinder. During downward movement of the piston deeper into the inner cylinder, liquid is displaced from the lower portion of the inner cylinder into the outer cylinder to provide an impact or shock absorbing effect.
During operation of the shock absorber, compressed air is aerated into the portion of the inner cyliner above the piston and degrades the shock absorbing effect. It is also necessary to displace liquid from above the piston into the outer cylinder during upward movement of the piston. To achieve this end, the above mentioned patent discloses a check valve which allows flow of air and liquid from the upper portion of the inner cylinder into the upper portion of the outer cylinder but not in the reverse direction. The check valve serves the dual function of removing air from the inner cylinder and allowing displacement of liquid therefrom during the upward movement of the piston.
However, several problems remain unsolved in the embodiment of the prior art check valve system. The check valve member tends to float during assembly of the shock absorber and is difficult to position in exact coaxial relation with the piston rod. As another drawback, the check valve member tends to fatigue at a junction of a base and resilient sealing edge portion thereof finally resulting in separation of the sealing edge portion from the base and failure of the check valve.